Scratch a mirror image of your itch to bring relief

Christoph Helmchen and his team at the University of Lübeck in Germany have found that a mirror illusion can fool people into feeling relief from an itch when scratching the wrong place.

The team injected the right forearms of 26 volunteers with itch-inducing chemical histamine. Sure enough, scratching the itchy arm did the trick, while scratching the other did not. Next, they used a mirror to block the person’s view of their itchy arm, reflecting the other limb in its place. When a researcher again scratched each arm, the itch diminished even when the unaffected, mirror-image arm was scratched. (PloS One, doi.org/q5r)

The relief from scratching the arm in the mirror is about a quarter of that from scratching the real itch, but the study shows that visual signals can override messages from the body if there is a mismatch between them.

Francis McGlone at Liverpool John Moores University, UK, thinks the finding could lead to treatments for chronic itching; a condition in which people will often scratch until their skin bleeds.